1. Field of the Invention
This invention relates to a process for producing polyisobutene with a high molecular weight at a higher temperature than the conventional polymerization temperature, using a catalytic system comprising a transition metal compound, a benzene derivative compound, and methylaluminoxane in non-halogenated solvent.
2. Background of the Related Art
Polyisobutene is generally produced by a cationic polymerization method at low temperature. Polyisobutene with a large molecular weight of more than 500,000 is reported to be produced at an extremely low temperature of lower than -80.degree. C. due to the instability of carbocationic active species of polymerization at higher temperature, according to the literature released by Kennedy et al. [("Polymer", 6, 579(1965)]. Catalyst used for producing polyisobutene has been selected from strong Lewis acids such as aluminum trichloride, boron trichloride and aluminum tribromide in halogenated solvent system comprising methyl chloride or dichloromethane.
However, such conventional polymerization method has some disadvantages in that (1) special facilities should be established due to the fact that polymerization is performed at an extremely low temperature, (2) heavy production costs are inevitably required for low temperature operation, and (3) chlorine-containing solvent used as a polymerization solvent causes the environmental problems.
In addition to the above mentioned method, another method of polymerizing isobutene using alcohol has been disclosed. Kennedy et al. have suggested a method for producing polyisobutene with molecular weight ranging from thousands to tens of thousands via a living polymerization using a variety of tertiary alcohols and boron trichloride as an initiator for polymerization ["Polymer Bulletin", 22, 455.about.462 (1989)]. Further, Toshiyuki et al. have disclosed a method of polymerizing isobutene using a catalytic system where some aromatic alcohol is combined to titanium tetrachloride (TiCl.sub.4) ["Macromolecules", 29, 6,100.about.6,103 (1996)].
Nevertheless, the process for producing polyisobutene in the presence of tertiary alcohol has encountered some problems in that excessive amount of tertiary alcohol should be added to monomer with a mole ratio of 1/100, since it is used as an initiator rather than an additive. Furthermore, boron trichloride which activate the initiator should be added in a high mole ratio of 1/10 to monomer. Another method for producing polyisobutene using aromatic alcohol has also faced disadvantages in its long-term storage and usage due to the instability of the catalytic system comprising transition metal-aromatic alcohol at room temperature.
Meantime, another method for producing polyisobutene using carboxylic acid has been disclosed. For example, M. Marek et al. have reported that isobutene has been very effectively polymerized at -20.degree. C. using hydrofluoric acid as an initiator, together with a co-catalyst such as titanium tetrachloride, titanium tetrabromide, vanadium tetrachloride, and boron trichloride [Makromol. Chem., 174, 1, (1973)]. Further, B. Matyska et al. have suggested a method for polymerizing isoprene in the presence of a catalyst such as trifluoroacetic acid, trichloroacetic acid, titanium trichloride, with a variation in activity according to acidity of catalytic system. [Collect. Czech Chem. Commun., 44, 1262, (1979)].
In the recent years, intensive studies have focused on the method of producing polyisobutene in non-halogenated solvent. For example, a method for producing polyisobutene with ten of thousands of weight average molecular weight has been disclosed using non-coordinated anions such as tris(pentafluorophenyl)boron as a co-catalyst and toluene as a polymerization solvent at a polymerizaiton temperature of -20.degree. C. (U.S. Pat. No. 5,448,001). Shaffer et al. have suggested that a polymer with a number average molecular weight of 140,000 can be obtained with 60% yield at -20.degree. C. in the presence of tris(pentafluorophenyl)boron, ["Journal of Polymer Science: Part A: Polymer Chemistry", 35, 329-344 (1997)]. The above results suggest that a non-coordination anion generated from a Lewis acid with a large size provides an extra stability of carbocationic active site in the polymerization of isobutene. In this context, research efforts to incorporate a suitable non-coordinating anion has been continuously given to achieve higher reaction temperature in the polymerization of isobutene with high molecular weight.